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This section discusses the BIOS settings that control the setup of IDE/ATA devices
(particularly hard disk drives). Most BIOSes have an entry in the Standard Setup menu for
each of the four IDE/ATA devices supported in a modern system (primary master, primary
slave, secondary master, and secondary slave). For each one, you can enter a value for
each setting in this section (type, size, cylinders, etc.) See here for details on hard disk geometries and data
structures.

It should be noted that all modern hard disks use special technologies that makes
simple geometry figures like "cylinders, heads, sectors" inapplicable. For
example, almost all modern drives use a variable number of sectors, and are set up using
an "approximate" figure in the system BIOS. This isn't something you generally
need to worry about as you set up your hard disk, but remember that if it says "63
sectors" that doesn't necessarily mean the drive really has that number in each
cylinder. In fact, it normally will not. This subject is covered in some detail in the section on hard disk geometry.

Virtually all BIOSes now come with IDE device autodetection. This comes in two forms:

Dynamic IDE Autodetection: This is the fully automatic mode. You set one
or more of the IDE devices (primary master, primary slave, etc.) on "Auto" and
the BIOS will automatically re-detect and set the correct options for the drive each time
you boot the PC. The BIOS will usually display on the screen what device it finds each
time it autodetects. For most people, this is the best way to go; it ensures that your
BIOS always has the correct information about your hardware, and it removes any
possibility of you installing a new drive but forgetting to set up the CMOS properly, or
of changing a parameter by mistake in the setup program. Not all BIOSes offer this setting
but most newer ones do.

Manual IDE Autodetection: This type of autodetection is run from the BIOS setup
program. You select autodetection, and the BIOS will scan the IDE channels, and set the
IDE parameters based on the devices it finds. When you save the BIOS settings, they are
recorded permanently. The disadvantage of this is that if you change devices, you must
return to the BIOS to re-autodetect the new devices (unlike the dynamic autodetection
scheme, which does a fresh autodetection each time you boot the PC). Virtually every BIOS
created in the last 8 to 10 years offers manual autodetection.

When you use dynamic autodetection, the BIOS will normally "lock" the
individual device settings that are being automatically set by the BIOS at boot time. Most
systems that provide manual autodetection will not lock the individual settings;
they autodetect, set the settings, and then let you change them if you want to. In most
cases of course, you will not want to change what the BIOS detects.

Most BIOSes that allow dynamic autodetection also allow manual autodetection; the
choice is yours. Using some sort of autodetection for IDE/ATA devices is strongly
recommended. It is the best way to reduce the chances of disk errors due to incorrect BIOS
settings. It also provides immediate feedback of problems; if you can't autodetect a drive
from the BIOS, you know you have
a problem even before you try to boot up.

Note: On most BIOSes, you
perform a manual IDE autodetection using a special entry with that name on the BIOS setup
program menu. This entry autodetects all IDE/ATA devices, one at a time. However, other
BIOSes "hide" autodetection. For example, on some BIOSes you autodetect an
IDE/ATA device by moving to the "Type" setting for the device and hitting
{Enter}. This runs the autodetection for that device only. Check your manual if you are
having problems finding the autodetection facility.

Warning: If your BIOS
contains a "hard disk utility" or "low-level format" type program, do
not use it on IDE/ATA drives. These utilities are intended for older MFM and RLL type
devices. Modern IDE drives do not need low-level formatting, interleave factor settings,
or media analysis under all but the very most unusual circumstances, and when they do need
it, they need special utilities specially designed for the type of drive you are using.